This invention relates to thermoplastic compositions which possess desirable heat resistance properties particularly, this invention relates to a melt-processable composition containing a crystalline polyphthalamide component and a particulate thermotropic liquid crystalline polymer component in an amount sufficient to nucleate a melt of the polyphthalamide, with or without reinforcing fibers, and to methods of improving the molding performance of polyphthalamide and fiber reinforced polyphthalamide compositions while maintaining the mechanical and thermal properties of the polyphthalamide or fiber-filled polyphthalamide compositions Molded articles prepared from these compositions exhibit excellent mechanical and thermal properties, including an especially high degree of crystalline homogeneity and high heat deflection temperature, even when molded using molds heated to temperatures below the glass transition temperature of the polyphthalamide component, often facilitating molding using steam or hot water-heated molds.
Commonly assigned U.S. Pat. No. 4,603,166 to Poppe et al., issued July 29, 1986, discloses polyphthalamide compositions which, when filled with glass fibers and molded, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above about 245.degree. C. (473.degree. F.). Included are compositions comprising recurring terephthalamide and adipamide or terephthalamide, isophthalamide and adipamide units and, preferably, wherein the mole ratio of dicarboxylic acid moieties provided by the terephthalamide, isophthalamide and adipamide units is about 65-90:25-0:35-5, respectively. As disclosed therein, such compositions, including particulate- and fiber-filled compositions, exhibit desirable thermal properties including deflection temperature, high tensile strength and flexural modulus and are useful in various applications including preparation of molded articles, fibers, and laminates.
Commonly assigned U.S. Pat. No. 4,617,342 to Poppe et al., issued Oct. 14, 1986, and commonly assigned, copending application Ser. No. 142,469 filed Jan. 8, 1988, and published European Patent Application No. 84300745 1 (Publication No. 0122688), published Oct. 24, 1984, disclose polyphthalamides which, when filled with glass fibers, have heat deflection temperatures at 264 psi, determined according to ASTM D-648, above 240.degree. C. Compositions according to U.S. Pat. No. 4,617,342 are prepared from dicarboxylic acid compounds comprising terephthalic acid and isophthalic acid compounds in a mole ratio of 80:20 to about 99:1 and diamines comprising hexamethylene diamine and trimethylhexamethylene diamine in a mole ratio of about 98:2 to about 60:40. Compositions taught in application Ser. No. 142,469 are based on terephthalic acid and isophthalic acid compounds in a mole ratio of about 70:30 to about 99:1 and hexamethylene diamine. Such compositions have utility in various applications, the neat and fiber-filled compositions being particularly suited for molding applications.
While such polyphthalamides filled with reinforcing fibers can be injection molded into articles having desirable mechanical and thermal properties, injection molding conditions for many of the polyphthalamides, and particularly those having a relatively high content of terephthalamide units (e.g., greater than about 50 mole percent) are often more severe than in the case of lower melting point polyamides such as poly(hexamethylene adipamide). Attainment of optimum properties in such polyphthalamide molded articles also can be complicated by molding conditions required to develop sufficient crystallinity in the molded polyphthalamides to achieve significant increases in heat deflection temperature and other properties dependent on crystallinity. In particular, the polyphthalamides have glass transition temperatures ("Tg") enerally ranging up to about 135.degree. C.; however conventional steam or hot water heated molds, which typically can reach temperatures up to about 100.degree. C., may be inadequate to allow for consistent development of sufficient crystallinity in many of the polyphthalamides to obtain significant property appreciation or may require undesirably long molding cycle times and higher mold temperatures to do so. 0f course, higher mold temperatures can be achieved with oil heated molds which can result in longer molding cycle times or annealing of molded articles can be conducted to increase crystallization and thereby enhance properties dependent thereon; however, both of these alternatives add cost and complexity to a molding operation. Accordingly, it will be appreciated that it would be desirable to modify such polyphthalamides to facilitate consistent attainment of heat deflection temperatures and other desirable properties in molding without sacrificing other desirable properties.
In general, it is known that modification of polymer properties may be accomplished in various ways. Modification of molecular structure through use of additional or different monomers in polymerization can lead to desirable improvements in some properties. However, the same often are accompanied by loss of other desirable properties and use of additional or different monomers is not always practical due to process considerations. In certain of the above-described polyphthalamides, replacement of terephthalamide units with adipamide units is effective to lower Tg of the compositions, thereby facilitating molding at lower mold temperatures; however, other properties, such as resistance to water absorption and thermal degradation are sacrificed. Use of additives may lead to property improvements without complicating a polymerization process; however the effects of additives often are unpredictable and, again, improvements in some properties often are achieved at the expense of other properties. For example, addition of plasticizers to the above-described polyphthalamides can result in lowering of Tg but this is achieved at the expense of mechanical properties such as modulus. Blending a given polymer with one or more other polymers may give compositions with a combination of properties intermediate those of the individual components; however, processing requirements often limit the number of candidates that can be blended with a given polymer in an attempt to attain desirable property modifications. Also, blending often is unpredictable; properties of a blend may reflect a desirable balance of the properties of its components or they may be better or worse than those of the components depending on compatibility of the components, reactivity thereof under blending or processing conditions and other factors.
The aforementioned U.S. Pat. No. 4,603,166 and U.S. Pat. No. 4,617,342 disclose that the polyphthalamides taught therein can contain fillers including minerals and fibers, preferably at levels of about 10-60 weight percent, for extending or providing reinforcement to the polyphthalamides. Disclosed particulate fillers include glass beads or glass spheres ranging from 5 microns to 50 microns in diameter, and fibrous mineral filler, such as, Wollastokup and Franklin Fiber with thickness, on average, between 3 microns and 30 microns. As can be seen from Example X of U.S. Pat. No. 4,603,166, heat deflection temperature of a polyphthalamide composition containing 40 or 60 weight percent of certain of these fillers was at most about 200.degree. C. U.S. Pat. No. 4,603,166 also discloses that the polyphthalamides can contain additives including heat stabilizers, UV stabilizers, toughening agents, flame retardants, plasticizers, antioxidants, and pigments. Example VII of the patent also discloses a nucleated, glass fiber-filled polyphthalamide composition containing 1.5 weight percent sodium phenyl phosphinate as a nucleating agent. The heat deflection temperatures thus obtained were at most about 145.degree. C.
U.S. Pat. No. 3,755,221 to Hitch, issued Aug. 28, 1973, discloses fast-cycling, rapidly moldable poly(hexamethylene adipamide) compositions containing 0.001-0.5 weight percent inert, particulate nucleating agent having average diameter less than 0.5 micron, 0.01-4 weight percent alkylene diamide derived from a C.sub.1-16 alkylene diamine and a saturated or unsaturated C.sub.12-20 monocarboxylic acid and 0.01-2 weight percent of a metal salt of a saturated or unsaturated C.sub.12-20 monocarboxylic acid. According to Hitch, the nucleating agent induces formation and growth of a crystalline texture characterized by reduction in spherulite size and in the degree of supercooling of the molten poly(hexamethylene adipamide) on cooling. It also is said to result in solidification of articles molded from the compositions at higher temperatures than otherwise would be the case, thereby reducing mold closed time and increasing production rates. Suitable nucleating agents are said to be any nucleating agent conventionally used in production of polyamides having a fine crystalline structure; disclosed examples include organic polymers of higher melting point than the polyamide or, preferably, an inorganic material such as talc, molybdenum sulfide, graphite or an alkali- or alkaline earth-metal fluoride, particularly calcium fluoride. The alkylene diamide included in the composities according to Hitch is said to function as a mold release agent; N,N'-ethylene-bis-stearamide is disclosed as a preferred alkylene diamide. The metal carboxylate component of Hitch's compositions is said to function as a lubricant that facilitates flow of the molten poly(hexamethylene adipamide). Zinc stearate is disclosed as a preferred material. Inclusion of up to 60 weight percent reinforcing agents such as glass fibers, by weight of polymer, also is disclosed. While Hitch discloses use of particulates to reduce cycle times in molding poly(hexamethylene adipamide) and glass fiber-filled compositions, the patent does not disclose the polyphthalamide component of the compositions of this invention nor does it address difficulties in molding of polyphthalamides requiring more severe molding conditions than poly(hexamethylene adipamide) The use of talc and the polyphthalamide component of the compositions of this invention is the subject matter of commonly assigned U.S. patent application Ser. No. 342,099 filed Apr. 21, 1989, in the name of David P. Sinclair, herein incorporated by reference.
Various additives have been proposed to crystallizable isotropic thermoplastics such as polyamides which are intended to improve the physical properties of fibers or films found therefrom. Such additives include inorganic materials, small organic compounds and large polymers with which the isotropic thermoplastic is coextruded or otherwise blended. With the discovery of thermotropic polyesters, as described, for example, in U.S. Pat. Nos. 4,140,846 to Jackson, Jr. et al. (Feb. 20, 1979), 3,890,256 to McFarlane et al. (June 17, 1975), 3,991,013 to Pletcher (Nov. 9, 1976), 4,066,620 to Kleinschuster et al. (Jan. 3, 1978), 4,075,262 to Schaefgen (Feb. 21, 1978), 4,118,372 to Schaefgen (Oct. 3, 1978) and 4,156,070 to Jackson, Jr. et al. (May 22, 1979), some proposals have been made to blend these materials with isotropic polymers. Unfortunately, such thermotropic polymers have thus far proved incompatible with isotropic polymers, with the heterogeneous blends that are formed exhibiting properties no better than the isotropic polymers alone.
In particular, M. Takayanagi et al. in J. Macromol. Sci.--Phys., B17(4), pp. 591-615 (1980) report attempts to blend nylon-6 or nylon-66 with wholly aromatic polyamides such as poly-p-benzamide or their block copolymers with nylon-6 or nylon-66. The wholly aromatic polyamides used are infusible.
Within the last two decades, the new class of polymeric materials which are called liquid crystalline polymers ("LCP"s) has been studied extensively. The anisotropic state of their solution (lyotropic liquid crystalline polymers, "LLCP"s) or melt (thermotropic liquid crystalline polymers, "TLCP"s) is between the boundaries of solid crystals and isotropic liquids. Tai-Shung Chung in "The Recent Developments of thermotropic Liquid Crystalline Polymers," Polymer Engineering and Science, July, 1986, Vol. 26, No. 13, pp. 901-919, herein incorporated by reference, describes this class of polymeric materials. TLCPs exhibit an anisotropic liquid state at temperatures in a range from about the melting point to the lower of either the clearing temperature or the decomposition temperature of the TLCP. This polymeric state is also referred to as a mesomorphic structure or a mesophase--a combined term adopted from the Greek language ("mesos" meaning "intermediate," and "morphe" meaning "form"). Upon melting a TLCP an anisotropic liquid state or mesophase is formed. It does not meet all the criteria to be a true solid or a true liquid, but it has characteristics similar to those of a solid and a liquid. For instance, the anisotropical optical properties of liquid crystalline polymeric fluids are like those of regular solids, but their molecules are free to move similar to liquids. The main difference between these polymers and the conventional liquid crystals used in electrical display devices is the molecular weight. LCPs have a much higher molecular weight. It is concluded by Chung, that the preparation of LCPs has been well developed by the industry, but that the understanding of the formation of LC domains has not been completely understood. The theoretical explanations for some unexpected results are still not available.
A. Siegmann et al. presented their study of a system composed of an amorphous thermoplastic polyamide matrix (Trogamid-T, Dynamite Nobel, West Germany) and a TLCP (aromatic copolyester based on 6-hydroxy-2-naphthoic acid and p-hydroxybenzoic acid, Celanese Corp. U.S.A.) in "Polyblends containing a liquid crystalline polymer", Polymer 26 1325 (1985), herein incorporated by reference. The viscosity of the blends was always much lower than that of the parent polymers. However, as is to be expected, the tensile mechanical behavior of these blends was very similar to that of polymeric composites. The rheological measurements were taken at 260.degree. C. (below the LCP melting). Siegmann et al. paper does not disclose the polyphthalamide component of the compositions of this invention.
Various LCPs have been claimed as processing aids for melt processable polymers, including fiber-forming aliphatic and aromatic polyamides, but improvement in processability, e.g., lowering of melt viscosity, is at the expense of a decrease in physical properties. As can be seen from Example 5 of U.S. Pat. No. 4,386,174, to Cogswell et al. issued May 31, 1983, or the same Example 5 of its continuation-in-part, U.S. Pat. No. 4,438,236, issued March 20, 1984, impact strength of a 90 parts nylon 6,6 with 10 parts LCP blend was only 1/3 the impact strength of nylon 6,6 without LCP. U.S. Pat. No. 4,386,174 does not disclose the crystalline polyphthalamide component of the compositions of this invention nor does the patent disclose any polyphthalamide compositions which posses improved heat resistance properties.
In U.S. Pat. No. 4,439,578 to Kim et al. issued Mar. 27, 1984, the inclusion of particulates of LLCPs having a high aspect ratio in thermoplastic molding compositions has been claimed to enhance the ability of the thermoplastic polymer to resist melt dripping in the standard UL94 vertical burn tests with bottom ignition,
Gabor D. Kiss disclosed tensile strength and Izod impact are decreased by blending of nylon with either LCP polyester or LCP esteramide (LCP content 30 weight percent) in "In Situ Composites: Blends of Isotropic Polymers and Thermotropic Liquid Crystalline Polymers" Polymer Engineering and Science, Mar., 1987, Vol. 27, No. 6. pp 410-423 at p 414. While Kiss discloses use of fibrous structures formed by thermotropic polymers to reinforce both crystalline and amorphous isotropic polymers, there is no suggestion of any nucleation process. Kiss does not disclose the crystalline polyphthalamide component of the compositions of this invention nor does he suggest any method to obtain polymer compositions which posses improved heat resistance properties.
Other patents and publications that may be of interest in connection with this invention in disclosing various polyamide compositions containing particulate materials are discussed below; none discloses the composition of this invention or suggests that the improvements achieved according to the invention might be achieved.
U.S. Pat. No. 4,292,416 to Shue et al., issued Sept. 29, 1981, while directed to blending of polyarylene sulfides with semicrystalline polyamides or copolyamides to obtain blends of improved molding performance, discloses that polyamides that do not normally contain sufficient crystallinity to attain desirable properties can frequently be improved in those properties through use of nucleating agents. Shue et al. discloses that suitable nucleating agents known in the prior art include finely divided organic or inorganic salts, silica, alumina and boron nitride and that it also is known that other polymers melting above the polyamide melting point can act as nucleating agents for the polyamide.
U.S. Pat. No. 4,501,844 to Chen et al., issued Feb. 26, 1985, and U.S. Pat. No. 4,536,533, also to Chen et al., issued Aug. 20, 1985, are directed to injection moldable, rapidly crystallizable compositions comprising a linear polyamide selected from poly(4,4'-methylenediphenylene azelamide), -sebacimide), -undecanediamide) and -dodecanediamide) and at least one material, selected from talc, sodium benzenesulfonate, polyethylene monomers, methacrylated butadiene-styrene polymers and certain multi-phase composite interpolymers, in an amount sufficient to promote crystallization of the polyamide. The patent notes that the art of increasing crystallization rate of certain polymers using specific nucleators is known but the art of crystallization is empirical and findings with one polymer cannot as a rule be applied to a different polymer. The polyamides used according to Chen et al. are normally amorphous in solid form unless annealed or heat treated. The crystallinity-promoting additive is used in amounts that can be determined by trial and error, according to Chen et al., generally ranging from about 0.1-20 weight percent based on weight of the polyamide and the crystallinity promoting additive. In the case of talc and benzenesulfonate as crystallinity-promoting additives, Chen et al. discloses that crystallinity is initiated at talc levels of about 0.1-5 weight percent and that both materials promote a surprisingly fast rate of crystallization in the polyamides. Compositions containing up to about 55 weight percent of a reinforcing agent or filler also are disclosed by Chen et al., inorganic and organic fibers, including glass and carbon fibers, being mentioned. Use of talc as a filler also is disclosed. Heat deflection temperatures at 264 psi of compositions according to Chen et al. are said to be extremely high, being in excess of 200.degree. C. and in some cases approximately 250.degree. C. Example 3 of the patents illustrates a composition with about 1 weight percent talc and 33 weight percent glass fibers having heat deflection temperature at 264 psi of 247.degree. C. when molded using a 138.degree. C. mold; however, heat deflection temperature at 264 psi of the composition molded using a 99.degree. C. mold was only 131.degree. C.
It is an object of this invention to provide polyphthalamide and/or fiber-filled polyphthalamide compositions of improved melt processibility. A further object of the invention is to provide such filled and/or unfilled compositions capable of being injection molded into articles having desirable mechanical and thermal properties. Another object of the invention is to provide such filled compositions capable of being molded into articles having such properties even when molded using molds heated at below Tg of the polyphthalamide so as to permit use of steam- or hot water-heated molds with a number of such polyphthalamides. Another object of the invention is to provide an improved process for molding such filled polyphthalamide compositions into useful fabricated products. A particular object of the invention is to provide fiber-filled polyphthalamide molding compositions which, when molded using a mold heated to within about 100.degree. C. of Tg of the polyphthalamide, have heat deflection temperatures at 264 psi according to ASTM D-648 substantially equal to those achieved when molded using a mold heated at Tg of the polyphthalamide. Other objects of the invention will be apparent to persons skilled in the art from the following description and claims.